Header only file and workflow update

[KalanaRatnayake]

• Combined "tinyxml2.cpp" and "tinyxml2.h" into "tinyxml2.hpp" which is a header only file for easier integration into ROS projects. Merging is done by copying the content directly and merging the namespaces. Changes are kept minimum (more optimizations can be done but not performed) due to easier future maintenance.
• Updated and formatted the Makefile to include additional test "xmltest2.cpp" that testes the new header file
• Updated CMakeLists.txt to include additional test "xmltest2.cpp"
• Updated ReadMe.md to include info about new file
• Updated workflow by removing ubuntu 20.04 because github have removed the runners
• Updated workflow by adding ubuntu 22.04 and 24.04 because github have added the runners
• Verified new file passes all the tests (makefile based, cmakelists.txt based and gitworkflow based)